Urban Weather Generator

urban heat island effect modeling software

Model Parameter Documentation

A note on the beta version

Please note that this beta version still requires users to input albedo and emissivity values in the template library before running the simulation. Thank you for trying it out!

construction

The building construction materials for wall, roof, and internal mass as well as urban road and rural site [these are in the advanced setting section] are defined by same parameter inputs in the <construction> tag. Glazing is also in this section.

Assembly

albedo

key design parameter: consider using green roof. A significant parameter determined by the sensitivity analysis [Boston], in conjunction with emissivity

definition Also known as reflection coefficient. It is the ratio of reflected radiation from the surface to incident radiation upon it. Affects sensible heat flux into boundary layer

emissivity

key design parameter: consider using green roof. A significant parameter determined by the sensitivity analysis [Boston], in conjunction with emissivity

definition Relative ability of the surface to emit energy by radiation. It is the fraction of energy radiated by a particular material compared to a black body. Affects sensible heat flux into boundary layer. Note: Visual surface color is not significant to total emissivity [surface color affects spectral emissivity at visible wavelength, which is negligible]

thermal conductivity [thermalConductivity]

volumetric heat capacity [volumetricHeatCapacity]

definition Also known as thermal mass. ability of a given volume of a substance to store internal energy while undergoing a given temperature change, but without undergoing a phase transition. It is density * specific heat

floor height [floorHeight] advanced setting

definition average of radiant fraction of the total building internal gains including people, light, and equipment, weighted by hourly internal load from each component. Internal gain can be split into sensible [radiant [mostly] and convective] and latent heat

definition average of latent fraction of the total building internal gains including people, light, and equipment, weighted by hourly internal load from each component. Internal gain can be split into sensible [radiant [mostly] and convective] and latent heat

cooling capacity of cooling system [coolingCapacity] advanced setting

efficiency of heating system [heatingEfficiency] advanced setting

definition effectiveness of a system in transforming the energy and power that is input to the device into an output. Efficiency is measured as a ratio of the measured performance to the performance of an ideal system

unit [--]; ranges between 0 and 1

typical values gas heating 0.8

daytime cooling setpoint [daytimeCoolingSetPoint] advanced setting

definition indoor setpoint for mechanical cooling system during the day

site coverage ratio [siteCoverageRatio]

key design parameter: affects canyon width; important especially when the site has tall buildings. Consider decreasing this parameter. A significant parameter determined by the sensitivity analysis [Boston, Basel, and Toulouse]

definition describes how close buildings are built in the city. Defined by ΣAbldg / Asite , where Abldg = building footprint and Asite = site area. This value can be extracted from the Grasshopper file

facade-to-site ratio [facadeToSiteRatio]

definition ratio of the vertical surface area [walls] to the urban plan area. Defined by ΣPhwtd / Asite, where P = building perimeter, hwtd = average building height, weighted by footprint, and Asite = total site area. Used to calculate canyon height and thus solar radiation received by building facade

sensible anthropogenic heat, other than from buildings [nonBldgSensibleHeat]

definition defines amount of heat released to urban canyon as sensible heat, mostly from traffic. Includes all sensible anthropogenic heat other than from buildings such as traffic, street lighting, and human metabolism

unit W/m2

typical values commercial area in Singapore 10, residential area in Singapore 4, Toulouse, France 8. Values are available for some cities by Sailor[5]

definition latent anthropogenic heat other than from buildings in the urban area

unit W/m2

typical values 0

neighborhood characteristic length [radius] advanced setting

definition radius of the urban area being modeled

unit m

typical values Street showed that 500m radius works best for Cambridge, MA[6], but this parameter is not as relevant, compared to other variables

Vegetation Properties

latent fraction of trees [treeLatent] advanced setting

definition characterizes the amount of latent heat given off by trees. Affects the moisture balance in the urban area

unit [--]; ranges between 0 and 1

typical values 0.7

latent fraction of grass [grassLatent] advanced setting

definition characterizes the amount of latent heat given off by grass. Affects the moisture balance in the urban area

unit [--]; ranges between 0 and 1

typical values 0.6

albedo of vegetation [vegAlbedo] advanced setting

definition Ratio of reflected radiation from the vegetation surfaces to incident radiation upon them

unit [--]; ranges between 0 and 1

typical values 0.25

vegetation participation begin month [vegStart] advanced setting

definition beginning month for vegetation

unit month

typical values 1 - 12

vegetation participation end month [vegEnd] advanced setting

definition end month of vegetation

unit month

typical values 1- 12

Boundary Layer Parameters

daytime boundary layer height [daytimeBLHeight] advanced setting

definition height of the urban boundary layer during daytime. The height is increases with the height of the buildings

unit [m]

typical values 700

nighttime boundary layer height [nighttimeBLHeight] advanced setting

definition height of the urban boundary layer during nighttime. The height is increases with the height of the buildings

unit [m]

typical values 80

reference height [refHeight] advanced setting

definition Reference height at which the vertical profile of potential temperature is vertical. It is the height at which the profile of air temperature becomes stable. Can be determined by flying helium balloons equipped with temperature sensors and recording the air temperatures at different heights

unit [m]

typical values 150

reference site [referenceSite]

latitude

definition latitude of the reference site

unit [o]

typical values n/a

longitude

definition longitude of the reference site

unit [o]

typical values n/a

reference site obstacle height [averageObstacleHeight]

definition height of objects that obstruct views to the sky at the weather station site, such as trees and buildings

unit m

typical values n/a

temperature measurement height advanced setting

definition the height at which temperature is measured on the weather station

unit [m]

typical values 2

wind measurement height advanced setting

definition the height at which wind speed is measured on the weather station

unit [m]

typical values 10

simulation parameters

start month [simuStartMonth]

definition start month of the simulation. UWG will morph the weather file for only the selected period

unit month in number format

typical values 1 - 12

start day [simuStartDay]

definition start date of the simulation. UWG will morph the weather file for only the selected period

unit date in number format

typical values 1 - 31

duration [simuDuration]

definition duration of the simulation. UWG will morph the weather file for only the selected period

unit number of days

typical values 365 [annual], 7 [week]

other resources

The values above have been validated with these resources. Please refer to these documentations for further details and other recommended values.